This invention relates to a method and an apparatus for geophysical exploration, and in particular to an improved method for detecting buried disseminated and/or massive sulphide or other mineralization by applying pulses of direct current to the ground while measuring the resulting alternating current magnetic fields set up within the zone of mineralization.
It is well known in the art of geophysics to prospect for buried zones of disseminated mineralization by means of the method known as "I.P." or "Induced Polarization". This method applies a series of abruptly terminated, high amplitude primary pulses of direct current to the ground while measuring the resistivety of the ground or measuring direct current flowing in the ground immediately after termination of the primary direct current pulses. This method has proven to be useful in detecting zones of disseminated mineralization but is relatively time consuming and expensive.
The present invention is based upon the discovery that a pulse or pulses of direct current applied to the ground in the vicinity of a zone of disseminated mineralization can cause an oscillation or alternating current within the zone of dissemination. The origin of such alternating current is not fully understood, but its existence has been established repeatedly in field measurements during and after application of the primary direct current pulse.
The discovery of this oscillation or alternating current results in many practical benefits. First, whereas in the conventional Induced Polarization method, the secondary currents measured are direct currents, in the present invention the secondary currents measured are oscillatory or alternating in nature and hence may be detected, amplified and otherwise electronically processed much more easily than is the case with the direct current measurements obtained with conventional Induced Polarization equipment. In addition, the present invention lends itself to remote sensing, e.g. performing surveys from moving vehicles such as trucks, boats or aircraft. Like Induced Polarization however, the present invention is useful in detecting the presence of zones of disseminated or massive sulphide mineralization.
According to one aspect, the invention consists of a method of and an apparatus for exploring the earth's crust for buried zones of massive or disseminated mineralization wherein the earth is energized by means of a pulse of direct current of predetermined amplitude and duration during and after which, measurements of alternating current magnetic fields are made.
With the foregoing objects in view, and other such objects and advantages as will become apparent to those skilled in the art to which this invention relates as this specification proceeds, this invention consists essentially in the arrangement and construction of parts all as hereinafter more particularly described, reference being had to the accompanying drawings in which: